The present invention concerns a process for increasing the flow rate at which an oil suspension is transported from the producing well by improving friction reduction. The process more particularly applies to underwater oil production, for example at offshore platforms.
Friction reduction through the addition of limited amounts of a water-soluble polymer was discovered by B. A. Toms in 1946. This is known as the “Toms effect” or “drag reduction”. This addition of a very small amount of a water-soluble polymer reduces hydraulic resistance when the fluid is circulating in a normally turbulent flow, thus improving its flow. Concretely, this can lead to improved flow in the pipeline, such as when pumping injection water in oilfields or in oil production when the amount of water produced increases over time as the well is in operation (when the watercut is greater than 80%, for example).
As the oil well operates, the amount of oil produced decreases and the amount of water retrieved increases. Obviously, for the same flow rate in the production pipeline, it becomes less profitable to operate the oilfields.
That is why it is necessary to increase the transport flow rate from the producing well in which the mixture of oil (and/or gas) and water from the injection circulates. For this, the “drag reduction” technique can be used to increase the water flow rate by 20 to 30% in the transport pipeline by adding small amounts of polymers into the oil-in-water suspension.
Document US 2005/0049327 A1 describes a process for reducing friction using an anionic hydrophilic polymer. This polymer can be added in the form of dispersion in a hydrocarbon or a water-in-oil emulsion, oil being a hydrocarbon.
Use of this “drag reduction” technique is of interest:                onshore, in transport lines when the producing wells are far from the separation facilities;        offshore, by injecting the polymer into the production pipeline on the sea floor at depths of 100 to 3,000 meters and over distances of up to several kilometers.        
In the latter case, a side pipe pumps the polymer in the form of an emulsion to the head of the producing well, with the polymer being dissolved along the line. The quantities injected amount to approximately 20 to 50 ppm and the pipelines and pumping systems are calculated for such amounts.
The most commonly used polymers are anionic polyacrylamides polymerized in reverse emulsion with a polymer concentration of approximately 30% by weight.
Reverse emulsions are characterized by the fact that:
1—Their viscosity is not Newtonian and decreases with shear stress.
2—Viscosity does not vary linearly with the polymer concentration.
If these installations are already in place, this operation is limited as the materials are calculated for a predetermined friction reduction. Furthermore, the temperature of seawater (approximately 4° C.) limits the flow rate in the installation.
One solution for increasing the flow rate of oil from the producing wells on an existing installation is therefore to inject more of the polymer.
Given that viscosity depends on concentration, a less viscous, and therefore diluted, emulsion must be supplied to the platform or FPSO (Floating Production Storage & Offloading unit) in order to inject more of the polymer. But in this case, the emulsion settles very quickly and forms viscous layers that solidify on the bottom of the transport containers. The installations on platforms or FPSOs are not able to re-homogenize it under local operating conditions. This solution therefore is not practically viable.
The technical problem that the invention proposes to solve, on an existing installation, is to inject more of the polymer into the production pipeline so as to increase the transport flow rate of oil from producing wells.